1. Field of the Invention
This invention relates to an improvement in document photographing cameras and in particular to improvements in devices for exposing recording index marks along the edges of the film when continuous form documents are being photographed.
2. Description of the Prior Art
Cameras are well known in the art which will expose onto the film, contemporaneous with the filming of the documents, machine readable index marks along the margin of the film such that the successive frames may be counted photoelectrically or afford a visible index on the film as the film is scanned. When photographing continuous form documents (fan-fold type) like that obtained as output from a line printer used with a computer system, to provide index marks along each page of this continuous form document, the prior art cameras have been provided with systems for placing index marks on the film as the film is moved. Prior art teachings of marking film are provided in U.S. Pat. No. 2,937,914; issued May 24, 1960 to Blake; U.S. Pat. No. 2,952,504, issued Sept. 13, 1960 to Path; U.S. Pat. No. 3,515,470, issued June 2, 1970 to Browder; and U.S. Pat. No. 3,902,802, issued Sept. 2, 1975 to Murata et al.
This latter mentioned patent discloses a photographing device for putting index marks on the film when lengthy web-form objects as well as short sheet documents are fed through the device. The photographing device is provided with a shutter controlled by pulse signals produced in response to the movement of the film for exposing the recording index marks on the film. This patent discloses a device for putting marks sequentially on the film when a continuous form document is being photographed as in the present invention but the manner of accomplishing this result is significantly different and not adapted to different formats of continuous documents. In this patented device pulses are generated from a light sensitive device to produce pulses as a slotted disc is driven past the light-receiving element which will control the shutter for exposing the film to the index markings. The spacing of the index marks on the film can be varied, as taught in the patent at column 5, lines 46 to 60, by changing the discs to substitute a disc wherein the position or spacing of the slits on the disc are different. This type of control does not afford a camera adaptable to the variety of sheet sizes for fan-fold type line printer output which are standardized within the United States and foreign countries per International Standards Organization Publication No. ISO2784.